This invention relates to a low firing barium-lead-titanate capacitor and a method for making that capacitor comprising firing the green ceramic body at a temperature less than the melting temperature of all the start materials, which start materials include a crystalline high-cadmium silicate flux.
It is known to use a low-melting-temperature sintering aid for reducing the temperature at which otherwise high firing ceramic materials such as the alkaline earth titanates will densify and mature. For example, my patent U.S. Pat. No. 3,885,941 issued May 27, 1975, describes the use as a sintering aid of multiple component cadmium-containing glasses having melting temperatures no higher than 875.degree. C. The cadmium and lead oxides in these glasses are highly toxic and volatile so that firing on an open slab leads to loss of these oxides from the sintering ceramic body to the surrounding atmosphere. This results in hazardous work conditions as well as degradation of the ultimate dielectric properties. Controlled atmosphere firing in closed containers is much safer and provides much better dielectric properties with tighter control, as is described in my patent U.S. Pat. No. 4,066,426, issued Jan. 3, 1978.
It is also known to combine and fire lead-lanthanum-titanate-zirconate (PLZT) ceramic powders with a low melting glass as is described in my U.S. Pat. No. 4,027,209 issued May 31, 1977.
All three of the above noted patents are assigned to the same assignee as is the present invention. Sintering aids known heretofore are usually glasses and are always designed to melt at the firing temperature to promote liquid phase sintering.
It is an object of the present invention to provide an efficient method for fluxing and promoting densification of a dielectric ceramic material at low firing temperatures with a minimum reduction in the resulting dielectric constant.
It is a further object of this invention to provide in such a method the use of a cadmium rich flux.
It is yet a further object of this invention to provide such a method capable of execution without the need for completely closed atmospheres and without substantial loss of cadmium to the atmosphere.
It is a further object of this invention to provide a dielectric body having a very high dielectric constant for any one standard class of temperature characteristics.